Background: Behavioral challenges such as poor emotional regulation, anxiety, and disruptive conduct increasingly impede secondary school students’ academic success and social functioning. Cognitive behavioral therapy (CBT) has demonstrated effectiveness in addressing maladaptive thoughts and behaviors, yet limited evidence exists on its application in Nigerian school settings.

Objective: This study examined the effect of a CBT‑based intervention programme on the behavioral adjustment and academic engagement of secondary school students in Port Harcourt Local Government Area (LGA), Rivers State, Nigeria.

Method: A quasi‑experimental pretest–posttest control group design was employed. Using stratified random sampling, 120 senior secondary school students were selected from four public schools and assigned to an experimental group (n = 60) and a control group (n = 60). The experimental group received an 8‑week CBT‑based intervention focusing on cognitive restructuring, emotional regulation, problem‑solving skills, and behaviour modification techniques. Data were collected using the Students’ Behavioural Adjustment Scale (SBAS) and the Academic Engagement Scale (AES), with Cronbach’s alpha reliability coefficients of 0.84 and 0.81 respectively. Data were analysed using mean, standard deviation, and analysis of covariance (ANCOVA) at α = 0.05.

Results: The experimental group demonstrated significantly higher post‑test scores in behavioural adjustment (Mean = 80.23, SD = 5.87) compared to the control group (Mean = 66.14, SD = 6.92). Similarly, academic engagement was substantially higher in the experimental group (Mean = 82.56, SD = 6.10) than in the control group (Mean = 69.02, SD = 7.03). ANCOVA results revealed a significant main effect of the CBT‑based intervention on behavioural adjustment [F(1,117) = 34.27, p <. 001] and on academic engagement [F(1,117) = 36.81, p <. 001].